PLASMA-CATECHOLAMINE AND VENTILATORY RESPONSES TO CYCLING AFTER PROPRANOLOL TREATMENT

The purpose of the present study was to examine the relationship betwe en minute ventilation (V-E) and plasma concentrations of epinephrine ( EPI) and norepinephrine (NE) during incremental cycling (20 W . 2 min( -1)) performed under conditions of beta-adrenergic blockade (80 mg of propranolol) and placebo in six untrained male subjects. No significan t differences existed between treatments in O-2 uptake, CO2 output, bl ood lactate, pH, or V-E during the submaximal work stages of increment al exercise common to both treatments (20-220 W). During exercise with beta-blockade, EPI, and NE concentrations were both significantly ele vated compared with control levels at every submaximal work stage. Sig nificant positive correlations between V-E and plasma levels of EPI an d NE were found during both beta-blockade (r = 0.98 and 1.00) and cont rol conditions (r = 0.98 and 0.96). Although the high correlations wer e unchanged during exercise with beta-blockade, the slopes of the regr ession lines for the V-E-EPI and the V-E-NE relationships were both si gnificantly reduced compared with control conditions. beta-blockade re sulted in elevated plasma levels of both EPI and NE compared with cont rol conditions without causing a change in exercise V-E. These finding s suggest that catecholamines may not be important substances in regul ating breathing during exercise.